*3.5. High-Throughput Metabolomics*

High-throughput metabolomics (HTM) is becoming a popular method for studying various metabolites resulting from activities of bacterial populations in microbiota. Metabolomics is the process of assessing the metabolite profile in any given sample or ecosystem [62]. This has been made possible by using methods such as high throughput mass spectrometry. Koening et al. [27] used gas chromatography-mass spectrometry (GC-MS) to measure the concentration of short chain fatty acids (acetate, butyrate and propionate) in fecal samples, which was then correlated with bacterial diversity of the gu<sup>t</sup> microbiota of infants. Similarly, Pires et al. [4] used mass spectrometry with direct infusion (DI-MS) on a Fourier transform ion cyclotron resonance instrument, to evaluate the chemical ecology of the gu<sup>t</sup> environment of urban and rural dwellers of the Amazon. The use of HTM in gastrointestinal microbiome study has been used to demystify the role of short chain fatty acid (propionic acid) in ameliorating multiple sclerosis disease in humans. Duscha et al. [63] investigated variations in microbiota and their associated short chain fatty acid metabolites and the effect of dietary propionic acid on immune-regulatory elements using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). It was revealed that propionic acid was greatly reduced in the serum and feces of multiple sclerosis patients compared with healthy controls. Conversely, the accumulation of specific short chain fatty acids has been associated with obesity, because they become additional

source of energy, thereby altering the balance of energy regulation [64]. Other metabolites, including polyunsaturated fatty acids linked with regulating several processes within the brain, bile acids, such as lithocholic acid, ursodeoxycholic acid and tauroursodeoxycholic acid and amino acid neurotransmitters such as glycine, aspartic acid, glutamic acid and gamma-aminobutyric acid (GABA), are metabolic products of the activities of gu<sup>t</sup> microbiota, which have been profiled by mass spectrometry based metabolomics [65]. Wilson and Forse [66] also developed an electronic-nose technology for early disease detection in microbial dysbiosis. These electronic-nose technologies have multi-sensor arrays and are able to analyze chemicals. Their invention could detect new groups of volatile organic compounds that are biomarkers metabolites also known as dysbiosis-associated disease markers, thereby providing a link between human ailments and resident microbes. The technology is noninvasive as it uses breath as sampling method. Gut metabolome is undoubtedly a peculiar candidate for the clinical diagnosis and managemen<sup>t</sup> of gastrointestinal diseases. However, it comes with attendant limitations. Smirnov et al. [67] identified some limitations of metabolomics in gu<sup>t</sup> microbiota research, including problems with sample handling, resulting in the loss of some metabolites due to freezing and thawing; drawbacks in personalized medicine/nutrition, due to the existence of variability in human microbiota and their metabolites; choice of adequate animal model and equipment. Improvement in sample handling and processing will prevent the loss of vital metabolites that otherwise would have not been accounted for. Furthermore, creating a database of metabolites associated with various members of the gu<sup>t</sup> microbiota will enhance the use of gu<sup>t</sup> metabolome in assigning biomarkers for the purpose of diagnosis, treatment and managemen<sup>t</sup> of gastrointestinal diseases by physicians.
